A leading cause of death in the United States today is coronary artery disease, in which atherosclerotic plaque causes blockages in the coronary arteries, resulting in ischemia of the heart (i.e., inadequate blood flow to the myocardium). The disease manifests itself as chest pain or angina. In 1996, approximately 7 million people suffered from angina in the United States.
Coronary artery bypass grafting (CABG), in which the patient's chest is surgically opened and an obstructed artery replaced with a native artery harvested elsewhere or a synthetic graft, has been the conventional treatment for coronary artery disease for the last thirty years. Such surgery creates significant trauma to the patient, requires long recuperation times, and causes a great deal of morbidity and mortality. In addition, experience has shown that the bypass vessel or graft becomes obstructed with time, requiring further surgery.
More recently, catheter-based therapies such as percutaneous transluminal coronary angioplasty (PTCA) and atherectomy have been developed. In PTCA, a mechanical dilatation device is disposed across an obstruction in the patient's artery and then dilated to compress the plaque lining the artery to restore patency to the vessel. Atherectomy involves using an end effector, such as a mechanical cutting device (or laser) to cut (or ablate) a passage through the blockage. Such methods have drawbacks, however, ranging from re-blockage of dilated vessels with angioplasty to catastrophic rupture or dissection of the vessel during atherectomy. Moreover, these methods may only be used for that fraction of the patient population where the blockages are few and are easily accessible. Neither technique is suitable for the treatment of diffuse atherosclerosis.
A more recent technique which holds promise of treating a larger percentage of the patient population, including those patients suffering from diffuse atherosclerosis, is referred to as transmyocardial revascularization (TMR). In this method, a series of channels are formed in the left ventricular wall of the heart. Typically, between 15 and 30 channels about 1 mm in diameter and up to 3.0 cm deep are formed with a laser in the wall of the left ventricle to perfuse the heart muscle with blood coming directly from the inside of the left ventricle, rather than traveling through the coronary arteries. Apparatus and methods have been proposed to create those channels both percutaneously and intraoperatively (i.e., with the chest opened).
U.S. Pat. No. 5,389,096 to Aita et al. describes a catheter-based laser apparatus for use in percutaneously forming channels extending from the endocardium into the myocardium. The catheter includes a plurality of control lines for directing the tip of the catheter. The patent states that because the myocardium is more easily traversed than the epicardium, the clinician may judge the depth of the channel by sensing the pressure applied to the proximal end of the catheter. The patent does not address the problem of cardiac tamponade that might result if the clinician inadvertently perforates the heart wall, nor how ablated tissue is prevented from embolizing blood vessels. Moreover, Aita et al. rely on fluoroscopic methods to determine the location of the distal end of the catheter. U.S. Pat. No. 5,380,316 to Aita et al. describes an intraoperative laser-based system for performing TMR.
U.S. Pat. No. 5,591,159 to Taheri describes a mechanical apparatus for performing TMR involving a catheter having an end effector formed from a plurality of spring-loaded needles. The catheter first is positioned percutaneously within the left ventricle. A plunger is then released so that the needles are thrust into the endocardium. The needles form small channels that extend into the myocardium as they are withdrawn. The patent suggests that the needles may be withdrawn and advanced repetitively at different locations under fluoroscopic guidance. The patent does not appear to address how tissue is ejected from the needles between the tissue-cutting steps.
The disadvantages of the above-described previously known methods and apparatus for performing TMR are numerous and will impede the acceptance of this new treatment method. For example, percutaneous laser-based systems, such as described in the Aita et al. patent, do not provide the ability to reliably determine the depth of the channels formed by the laser and may result in perforations, nor does that system address potential embolization by the ablated tissue. Laser ablation also causes a significant degree of thermal damage to surrounding tissue, which may be undesirable. In addition, the use of fluoroscopy to determine the exact position of the laser tip within a beating heart is inexact at best. Likewise, previously known mechanical systems such as described in the Taheri patent do not address issues such as rebounding of the needle away from the ventricle wall during deployment or how to remove tissue cores from the needles, and again rely on fluoroscopy to determine the location of the distal tip of device within the heart.
In view of the shortcomings of previously known TMR devices, it would be desirable to provide apparatus and methods for performing percutaneous surgery, such as TMR, that permit precise control of the end region of the device carrying the end effector. Such precise control desirably should, in the context of TMR, include the capability to reliably control the depth of channel formed in the myocardium by the end effector. It would also be desirable to control the location of the end region of the device within the ventricle both with respect to features of the ventricular walls and in relation to other channels formed by the device. In addition, such precise control preferably should include the capability to stabilize the end region of the device within the organ, for example, to counteract reaction forces created by the actuation of the end effector during treatment.
It would also be desirable to provide apparatus for percutaneously performing surgery within a hollow-body organ, such as the heart, that provides for evacuation of tissue removed from the interior of the organ to prevent embolization thereof. It would therefore be desirable to provide an end effector that enables tissue removed from the treatment site to be aspirated.
A number of devices are known in the medical arts that provide certain aspects of the desired functionality. For example, U.S. Pat. Nos. 5,389,073 and 5,330,466 to Imran describe steerable catheters; U.S. Pat. No. 5,415,166 to Imran describes a device for endocardial mapping; U.S. Pat. No. 4,813,930 to Elliott describes a radially extendable member for stabilizing an angioplasty catheter within a vessel; U.S. Pat. No. 5,354,310 describes an expandable wire mesh and graft for stabilizing an aneurysm; and U.S. Pat. Nos. 5,358,472 and 5,358,485 to Vance et al. describe atherectomy cutters that provide for aspiration of severed material.
None of the foregoing references, for example, overcomes problems associated with locating an end region of a catheter against a position on the inside wall of a heart chamber. Moreover, the prior art is devoid of a comprehensive solution to the above-noted shortcomings of previously-known apparatus for percutaneously performing surgery, and especially for performing TMR.